1. Field of the Invention
The present invention relates to a magnetic bubble store. It is applicable to the storage of binary information or bits, materialized in the form of isolated magnetic domains, called bubbles. These domains have the opposite magnetization to that of the remainder of the magnetic material constituting the layer in which they are formed.
Each bubble can be displaced by a force and movement can take place freely in any direction in the plane of the magnetic layer. The magnetic layer is a magnetic garnet and the bubbles are formed in said layer by applying a d.c. magnetic field thereto perpendicular to the plane of the layer. This field is in practice produced by a permanent magnet and ensures the non-volatility of the data contained in the store.
The magnetic garnet layer in which the bubbles are formed is generally supported by a non-magnetic, monocrystalline garnet.
2. Description of the Prior Art
It is known to displace the bubbles by applying a rotary magnetic field, whose function is to create poles on e.g. permalloy motifs or patterns, having the shape of T-bars, chevrons or half-disks. As result shift registers are obtained in which the binary information is represented by the presence "1" or the absence "0" of a bubble. In addition to these permalloy motifs it is known that it is necessary to use electrical conductors for producing on the bubble store chip writing, data recording, non-destructive reading, transfers between registers and erasure functions. Erasure is performed in bitwise manner by the selective or overall destruction of the bubbles. This erasure is obtained very simply by increasing the value of the d.c. magnetic field beyond the maximum value permitted for the recording.
In order to displace the bubbles in the magnetic garnet layer two methods are at present used, whereby the bubbles can be displaced either by an electrical current or by a magnetic field.
The best known magnetic bubble store types are described below.
Stores constituted by a single looped register, which can be called series organization stores in which there is a single, very long, looped shift register are known. This register is provided with a single access station able to give access to only one bit at once. Although very simple, this type of store requires a very long access time and does not permit any random access. The absolutely perfect manufacture thereof is required. Thus, any defect can lead to an interruption in the chain or string of bubbles representing the data contained in the store.
Stores having an organization into "minor-major registers" are also known. These stores comprise a system of recording loops called "minor registers," making it possible to record data. Another loop called the "major register" comprises the access station. The minor registers are longitudinally juxtaposed and the major register is oriented transversely. The magnetic bubbles contained in the minor registers can be transferred into the major register via transfer gates. These gates make the structure and manufacture of the store more complicated. In addition, the access time is high, because the magnetic bubbles can pass through the entire length of the major register before reaching the access station, then follow an equivalent path for their return into the minor registers. Finally the displacement in the minor register is unidirectional as a result of the synchronization contraints in the propagation of the bubbles between the minor registers and the major register.
Bubble stores comprising a series of shift registers or minor registers arranged in longitudinal manner and a transversely positioned major register are known. In this type of store the major register is called an access contour or outline and is incorporated into the minor registers which thus participate by at least two bits in the access outline. In this case the influence of the access outline can be prejudicial on the adjacent bubbles. Thus, by creating the magnetic field gradients necessary for the displacement of the bubbles on this access outline there can be a weakening of the adjacent bubbles in the store area in question.
In the case of the two latter store types, which generally use minor registers constituted by permalloy motifs shaped like a T, chevrons or half-disks, it is impossible to ensure a transfer of the bubbles from one minor register to another. In the case of half-disks motifs the distribution of the magnetic potentials along the major register is not homogeneous and during the transfer of the bubbles along the major register there are discontinuities in the field which can lead to a weakening of the bubbles.
Finally the Expert has often considered it to be important to only have a single access point between a minor register and a major register, without it hitherto being possible to produce a store fulfilling this condition.